The shrinking size of electronic equipment demands increasing power density of the supplying system. The switching power supply based on the principle of pulse width modulation is better suited for efficient power control and has become more prevailing. FIGS. 1 and 2 show two types of conventional resonant switching power supplies. Those resonant switching power supplies use resonant circuits composed of inductor and capacitor to generate sinusoid wave, and the zero cross points of the sinusoid wave to provide zero-voltage switching (ZVS) or zero-current switching (ZCS). This technique can be roughly classified as serial load resonant (SLR) as shown in FIG. 1 and parallel load resonant (PLR) as shown in FIG. 2. In the above two types of circuit, the frequency of the input voltage is designed to be the same as the resonant frequency as the resonant circuit to provide the most efficient output. However, the optimal operation relies on the assumption of constant load, this is rare in practical situations.
Another conventional resonant switching power supply, is a full bridge ZVS PWM converter. The full bridge ZVS PWM converter uses four sets of switches. Therefore, the circuit is complicated and the parasitic capacitance and leak inductance is hard to manipulate, thus being difficult to mass produce. Moreover, this full bridge ZVS PWM converter is not economic in light load application, especially hard to ensure zero-voltage switching (ZVS) or zero-current switching (ZCS) in a light load application,
Therefore, the present invention is intended to provide a resonant switching power supply with zero voltage and zero current switch feature, which can be operated in a half-bridge or a full-bridge scheme.
It is an object of the present invention to provide a resonant switching power supply with zero voltage and zero current switch features, whereby the power consumption is reduced and electromagnetic radiation is minimized.
It is another object of the present invention to provide a resonant switching power supply which has the advantages of low-cost and convenient manufacture and can be mass-produced to meet the requirement of various loads.
It is still another object of the present invention to provide a resonant switching power supply which will not be influenced by the parasitic capacitance and leak inductance.